Decrease In Crosslink Density Research Articles

Influence of Lowering the pH Value on the Generation of Fibrous Structures of Protein Gels with Different Network Types.

High-moisture extrusion of plant proteins to create meat-like structures is a process that has met with increasing attention in the recent past. In the process, the proteins are thermomechanically stressed in the screw section of the extruder, and the resulting protein gel is structured in the attached cooling die. Various protein sources, notably soy protein isolate (SPI) and wheat gluten, are used to form gels with different networks: SPI creates a physical, non-covalent network, while gluten forms a chemical, covalent one. The food industry frequently adds weak acids to modify taste and shelf life. However, it is known that a change in pH affects the gelation behavior of proteins because the repulsive forces within and between the proteins change. The research reported here was carried out to investigate for the two proteins mentioned the influence of pH modification by the addition of citric acid and acetic acid on gel formation and the meat-like structures produced. For this purpose, materials and parameters were screened using a closed cavity rheometer, followed by extrusion trials at pH 7.36-4.14 for SPI and pH 5.83-3.37 for gluten. The resulting extrudates were analyzed optically and mechanically, and protein solubility was tested in a reducing buffer. For both protein systems, the addition of acid results in less pronounced meat-like structures. At decreasing pH, the complex viscosity of SPI increases (from 11,970 Pa·s to 40,480 Pa·s at 100 °C), the generated gel becomes stronger (strain decreased from 0.62 to 0.48 at 4.5 × 105 Pa), and the cross-linking density grows. For gluten, a decreasing pH results in altered reaction kinetics, a more deformable resulting gel (strain increased from 0.7 to 0.95 at 4.5 × 105 Pa), and a decreased cross-linking density. Solubility tests show that no additional covalent bonds are formed with SPI. With gluten, however, the polymerization reaction is inhibited, and fewer disulfide bonds are formed.

Nucleophilic amino acids as a renewable alternative to petrochemically-derived amines in glycerol epoxy resins

The standard epoxy resin curing agents revealed are from unsustainable petroleum-based sources, which produce poisonous exhaust when cured. Amino acids, a bio-based epoxy curing agent with amino and carboxyl groups, are another potential curing agent. Water-soluble epoxy resins cured with lysine (Lys), glutamic acid (Glu), leucine (Leu), and serine (Ser) as amino acids were investigated. The results showed that the water-soluble epoxy resin (glycerol epoxy resins, GER) was cured with Lys and Glu after reacting. Fourier transform infrared (FT-IR) spectroscopic analysis of the GER-Lys showed that the amino and carboxyl groups of Lys primarily reacted with the epoxy groups of GER. The elongation at break of Lys-cured GER (GER-Lys) cured at 70 ℃ with a molar ratio of 1꞉0.75 was 75.32%. The fact that elongations at break of GER-Lys (79.43%) were higher than those of GER-Glu (17.33%), respectively supports the decrease of crosslinking density by the amino acid-cured GER reaction. The potential of Lys and Glu alternatives for petrochemical amines is demonstrated and provides promising opportunities for industrial application.

Effect of localized control of cross-link density on mechanical properties of bicontinuous cubic lyotropic networks via copolymerization with different singly-polymerizable monomers

Two singly-polymerizable analogs of a bicontinuous cubic (Q) phase, lyotropic liquid crystal (LLC) (i.e., amphiphilic) cross-linking monomer were designed and synthesized as phase-compatible, non-cross-linkable co-monomers. These were copolymerized with the parent, single-head/single-tail cross-linking monomer to locally control the cross-link density in either the hydrophobic tail or hydrophilic headgroup regions of the Q phase and study their effect on the mechanical properties of the resulting polymer networks. Structure-property relationships were elucidated: (1) Blends with smaller amounts of the parent cross-linking monomer relative to non-cross-linkable analog exhibit progressively lower endpoint stress and Young's modulus values. (2) A decrease in cross-link density also influences the pliability of each sample as there appears to be a threshold (i.e., minimum) cross-link density that must be exceeded before stretchability is significantly affected. (3) Each LLC-based structural motif tolerates different levels of non-cross-linkable analog, shifting the stress-strain behavior of these cross-linked Q-phase materials.

Probing the Solubility of Imine-Based Covalent Adaptable Networks.

Covalent adaptable networks (CANs) are polymer materials that are covalently cross-linked via dynamic covalent bonds. The cross-linked polymer network is generally expected to be insoluble, as is seen for traditional thermosets. However, in recent years, it has become apparent that-under certain conditions-both dissociative and associative CANs can be dissolved in a good solvent. For some applications (e.g., those that require long-term (chemical) stability), the solubility of CANs can be problematic. However, many forget that (selective) solubility of CANs can also be applied advantageously, for example, in recycling or modification of the materials. In this work, we provide results and insights related to the tunable solubility of imine-based CANs. We observed that selected CANs could be fully dissolved in a good solvent without observing dissociation of imines. Only in an acidic environment (partial) dissociation of imines was observed, which could be reverted to the associated state by addition of a base. By adjusting the network composition, we were able to either facilitate or hamper solubility as well as control the size of the dissolved particles. DLS showed that the size of dissolved polymer particles decreased at lower concentrations. Similarly, decreasing cross-linking density resulted in smaller particles. Last, we showed that we could use the solubility of the CANs as a means for chemical recycling and postpolymerization modification. The combination of our studies with existing literature provides a better understanding of the solubility of CANs and their applications as recyclable thermosets.

Toward soluble high-performance electrochromic polymer: Optimizing cross-link density

Cross-linked conjugated polymers attract great attentions in optoelectronic field due to their unique properties resulting from the existence of intramolecular pore and network structure. However, the poor solubility restricts the application of cross-linked polymers in photoelectric device. Here, the strategy of changing cross-link density is employed to optimize solubility and properties of cross-linked conjugated polymer. Five polythiophene derivatives with different cross-link densities were synthesized through direct arylation reaction. The cross-linked conjugated polymers achieve good solubility in organic solvent through decreasing cross-link density, and possess similar optical absorption regions compared to conjugated polymer without cross-linked structure. Through optimizing cross-link density, the electrochromic properties of conjugated polymers could be enhanced, including optical contrast (55 %), response time (0.6 s), coloration efficiency (CEox = 510 cm2 C-1; CEred = 3567 cm2 C-1), and stability, which is more excellent than that of reported cross-linked polymers. And, the flexible electrochromic device based on PET-(1,9) was constructed by simple solution processing and could achieve fast color change between wine red and light blue in low voltage driving force, which indicating the applicability of soluble cross-linked conjugated polymer. Besides, the mechanism about ionic transport and stability improvement of cross-linked conjugated polymers is discussed. These results demonstrate that changing cross-link density is an effective strategy to optimize the properties of cross-linked conjugated polymers.

Effect of chain extender dichlorodimethylsilane (DDS) on the mechanical properties of hydroxyl terminated polydimethylsiloxane (HOPDMS)

The effect of the chain extender dichlorodimethylsilane (DDS) on the mechanical properties of hydroxyl terminated polydimethylsiloxane (PDMS) was investigated. Different amounts of DDS ranges from 0.5 to 5.0 phr were added to the base polymer. After degassing (degasification) the prepared solution of chain extender (DDS) for 5h, viscosity was measured. It was observed that viscosities were increased from 1189 to 212246 cst (almost 180 times), while their molecular weights increased from 13899 to 206019 g/mol (almost 15 times) at 3.5 phr DDS concentration. Crosslinking agents such as tetraethoxysilane [tetraethyl orthosilicate (TEOS)] and tin catalyst were utilized for fabricating the sheet. Mechanical properties were evaluated by using universal testing machine. Tear strength was increased from 0.057 to 0.352 N/mm while Tensile strength was decreased from 0.40 to 0.23 MPa % and elongation at break was increased from 38.87 to 552.20%. Durometer shore A was utilized to measure hardness of the thin films which was decreased from 25 to 10 shore A. Swelling measurement indicated that crosslinking density was decreased from 3.6x10−4 to 1.1x10−5 mol/cm3, while molecular weight between crosslinks was increased from 2979 to 89597 g/mol. Increase in viscosity, molecular weight and average molecular weight between junctions and decrease in crosslinking density with the addition of dichlorodimethylsilane as chain extender confirmed the chain extension of low molecular weight PDMS. Results showed that maximum outcome in physical and mechanical properties of cured PDMS were obtained at 3.5 phr DDS concentration. Relation between tear strength and average molecular weight between junctions obeyed the lake and Thomas equation.

Improvement in the toughness and adhesive properties of cyanate ester resin by incorporation of fluorinated poly(aryl ether nitrile)

AbstractCyanate ester (CE) resins possess excellent thermal and mechanical characteristics, yet their brittleness and high cross‐link density limit their practical application. To overcome this limitation, the modification of CE with thermoplastic resins has been employed as an effective strategy to enhance their toughness and mechanical properties. In this study, a novel fluorinated poly(aryl ether nitrile) (PFPEN) with excellent solubility and thermal properties was synthesized through a nucleophilic substitution reaction. The effect of the addition of PFPEN on a blend composed of bisphenol A cyanate ester (ACE) and a mixed catalyst was investigated. Differential scanning calorimetry results showed that the addition of PFPEN facilitated the curing reaction of ACE, resulting in a lower exothermic peak temperature. Compared to the pure ACE, the addition of PFPEN at 20 phr significantly improved the tensile and impact strengths of the resin, as well as enhanced the lap shear strength at room temperature by 36% and the peel strength by 320%, respectively. The scanning electron microscope results showed a ductile fracture mechanism. However, it should be noted that the decrease in crosslinking density resulting from the addition of PFPEN may affect the lap shear strength at 300°C and the glass transition temperature (Tg) of the material.

Inactivation of Staphylococcus aureus in gelatin nanoparticles using supercritical carbon dioxide

Nanoparticles (NPs) are widely studied for biomedical applications. Generally, NPs and NP-based materials should be effectively sterilized without altering their structure and function before clinical translation can be considered. However, research on industrially scalable sterilization methods of nanoparticles is still scarce. Therefore, we explored if treatment of gelatin nanoparticles (GNPs) using supercritical carbon dioxide (scCO2) resulted in effective inactivation of Staphylococcus aureus as frequent pathogen causing infections. After scCO2-treatment the morphology, size and surface charge of GNPs remained unchanged, although a slight decrease in crosslinking density was observed. ScCO2 successfully inactivated Staphylococcus aureus in GNPs, as evidenced by a 12-log reduction in bacterial burden. However, cytocompatibility of GNPs was lower after scCO2 treatment, indicating that the process still requires further optimization. Nevertheless, the work presented herein highlights the strong potential of scCO2 for inactivation of pathogens in nanoparticles.

Novel photosensitive resin simultaneously with outstanding cryogenic strength and toughness for digital light processing three-dimensional Printing

With the increased demand for three-dimensional (3D) printing technology in various fields, it is important to develop high-performance resin that could withstand temperature changes to expand their application potential. A new photosensitive oligomer (BDM–DDM–ETPS–GMA) based on epoxy-terminated polyether siloxane (ETPS) and bismaleimide diphenylmethane/4, 4′-diaminodiphenylmethane (BDM–DDM) resin was synthesized and then mixed with other oligomers, reactive diluents, and photoinitiators to prepare a novel 3D printing resin. The results show that the resulting resins exhibit good fluidity and rapid photopolymerization ability, which satisfies the rheological prerequisites of 3D printing resin. Moreover, the incorporation of BDM–DDM–ETPS–GMA can simultaneously improve the cryogenic stiffness and toughness of commercial resin. Specifically, the tensile strength, elongation at break, flexural strength, impact strength, and storage modulus at −30 °C of modified resin with 15% BDM–DDM–ETPS–GMA are 151.2 MPa, 10.9%, 146.2 MPa, 9.8 kJ/m2, and 4,131 MPa, respectively, which are about 2.81, 1.70, 1.37, 1.81, and 1.54 times of that of commercial resin. A synergistic enhancement mechanism is believed to be attributed to these results, which includes the introduced flexible siloxane chain and the rigid bismaleimide structure as well as decreased cross-linking density. These attractive features of modified resins suggest that the method proposed herein is a new approach to develop high-performance 3D printing photosensitive resin simultaneously with outstanding cryogenic strength and toughness and thus has wide application potential in the aerospace, military industry, and other cutting-edge fields.

Improving toughness of epoxy resin by in‐situ formed secondary network during tertiary amine initiated curing

AbstractThe mechanical properties of epoxy resin cured by tertiary amine initiated ring‐open reaction were investigated. Special curing procedures that first at 130°C for different times (facilitating chain transfer/reducing crosslinking density) and then 80°C/2 h–130°C/2 h were used. For cured specimens, the glass transition temperature showed a continuous decrease with increasing time at the first step of curing (t1st step), and the swelling ratio also increased. These changes pointed to a monotonic decrease in crosslinking density. Mechanical properties were characterized by three‐point bending and tensile test. Both the deflection and strain at break showed a sudden increase when t1st step reached 30 min, corresponding well to occurrence of gelation at 130°C. The fracture surface after tensile test was further examined. Rough surface with rupture of fibrillar structure was found when t1st step reached 30 min. These observations all suggest an abrupt increase of toughness related to gelation (t1st step = 30 min). It is explained by formation of network at the first step of curing, which has lower crosslinking density and serves as a secondary toughening network.

The role of molecular architecture on the viscoelastic properties of thermoreversible polyurethane adhesives

New polyurethane (PUR) adhesives containing covalent Diels-Alder (DA) bonds that can break and form with temperature have been recently developed for sustainable multilayer packaging. The understanding of the mechanical properties and in particular of creep in terms of molecular architecture appears of outmost importance in view of their applications and potential reutilization. Oscillatory shear rheometry shows a modulus decrease with temperature associated to bond breakage and the enhancement found upon cooling can be associated with network reconstruction. Analysis of storage modulus values above the glass transition and below the retro-DA reaction suggests a lower network crosslinking density with increasing adduct content. Room temperature indentation and shear rheometry tests reveal that DA bonds improve the modulus and reduce the resistance to linear viscoelastic flow. The modulus improvement can be associated to the enhanced chain rigidity introduced by the DA moieties and the reduced creep resistance seems to be related to the decrease of crosslinking density.

Research on modification mechanism and performance of an innovative bio-based polyurethane modified asphalt: A sustainable way to reducing dependence on petroleum asphalt

• An innovative BPMA was synthesized by BPU and VB. • BPU and VB are chemically crosslinked by urethane bond, resulting in satisfactory compatibility of BPMA. • BPU exhibits an appropriate crosslinking density, which results in an improved ductility of BPMA. • BPMA shows a suitable construction allowance time and good working performance. Sustainable bio-oil, as a modifier and partial substitute for asphalt binder, is potentially reducing dependence on non-renewable petroleum asphalt in pavement engineering. However, unsatisfactory performance of bio-oil asphalt dramatically hinders the application of bio-oil in pavement engineering. In this paper, bio-oil based polyurethane modified asphalt (BPMA), an innovative way of modifying bio-oil asphalt binder, was explored to prepare a sustainable asphalt binder with satisfactory performance. BPMA was synthesized by virgin asphalt and bio-based polyurethane (BPU), in particular, BPU was pre-assembled by castor oil, isosorbide, and isocyanate. The formulation and synthesis process of BPU were investigated via mechanical property test and fourier transform infrared spectroscopy (FTIR). Attributed to the addition of isosorbide, BPU exhibited a significant decrease in crosslinking density and a remarkable improvement in ductility. Furthermore, BPMA containing various contents of BPU at different curing duration were systematically studied by rotational viscosity, storage stability, fluorescence microscopy, FTIR, dynamic shear rheometer and bending beam rheometer to evaluate workability, compatibility, modification mechanism, working performances. Results showed that BPMA exhibited suitable workability, good compatibility, and satisfactory working performance. Moreover, the microstructure of BPMA transformed from VB-phase dominated island structure to BPU-phase dominated spatial network structure as BPU content increased. FTIR results indicated a combination modification mechanism of physical modification (effect of BPU) and chemical modification (chemical crosslinking between BPU and VB).

Mechanochemical modification of crosslinked low‐density polyethylene: Effect of solid‐state shear pulverization on crosslinks, branches, and chain lengths

AbstractCrosslinked low‐density polyethylene (XLLDPE) is widely used in several specialty plastics industries. However, the permanent chemical crosslinks cause high‐melt viscosity and poor processability, preventing the material from being reused and recycled effectively. This study investigates solid‐state shear pulverization (SSSP) as a continuous, commercially viable mechanochemical processing technique to initiate the decrosslinking of XLLDPE for mechanical recycling. Post‐industrial XLLDPE scrap material was processed using SSSP with a range of pulverization conditions, which were correlated with universal processing covariants of specific mechanical energy and particle size distribution. The physical properties of SSSP‐processed materials were compared to as‐received XLLDPE and uncrosslinked low‐density polyethylene. While gel content tests confirm a gradual decrease in crosslinking density with a more energy‐intensive SSSP process, melt rheology and dynamic mechanical analysis characterization revealed additional chain architecture modifications such as branching and chain scission. Based on differential scanning calorimetry and thermogravimetric analysis, the SSSP‐processed XLLDPE retained its thermal stability and crystallinity; tensile testing results showed improved stiffness, strength, and toughness. These results indicate that tunable SSSP can transform XLLDPE into a decrosslinked, branched, and melt‐processable recycled polyethylene.

Exploring the effects of cardanol-based co-curing agents with different phosphorus structures on the mechanical and flame-retardant properties of bismaleimide resin

Aiming to address the problems of flammability and brittleness of BMI and reduce the use of petroleum-based materials, three kinds of cardanol-based co-curing agents (CDPO, CDPC, CDCP) were synthesized and applied to prepare advanced BMI. Compared to the neat BMI, the modified BMI exhibited better thermal stability with higher decomposition temperatures and char yields. The BMI/CDCP-10 containing 4.5 wt% CDCP possessed the best flame retardancy with 50.4% reduction in PHRR, 27.5% reduction in THR and 21.2% reduction in TSP compared to those of neat BMI. Moreover, with the 4.5 wt% incorporation of CDPO, CDPC and CDCP, the impact strength of BMI was enhanced by 95%, 133.8% and 127.5% respectively, due to the flexible fatty chains and the decreased crosslinking density. The reason for different modification effects among modified BMI systems is studied from the structure of modifiers, finding that the phosphorylated cardanol with higher content of O and higher valence of P can be utilized to improve the mechanical property and fire safety of BMI. This work provides a new way to reduce the dependence on the petroleum-based materials and expand the application areas of BMI.

Synthesis, physicochemical, and antimicrobial characteristics of novel poly(urethane-siloxane) network/silver ferrite nanocomposites

In situ polymerization was used to produce novel AgFeO2@PEG/polyurethane network nanocomposites (NP-PUs) with 30–60 wt% of soft poly(dimethylsiloxane) segments in polyurethane (PU), containing 1 wt% of PEG-coated AgFeO2 nanoparticles, AgFeO2@PEG. Physicochemical properties and in vitro biological activity of the NP-PUs were systematically evaluated in terms of AgFeO2@PEG (NP) addition and soft segment content. High-angle annular dark-field transmission electron microscopy showed that the nanoparticles were generally uniformly distributed in the PU matrix. Increased soft segment content caused significantly increased intensity of the broad, amorphous X-ray diffraction peaks of crystalline AgFeO2, probably because the chemical composition of PU affected the distribution of nanoparticles. The Young modulus, hardness, and plasticity of the NP-PUs were higher than for pure PU and increased with decreasing soft segment content. Decreased soft segment content induced higher microphase separation, increased hydrophilicity and swelling ability, but decreased cross-linking density. Additionally, NP-PUs had higher glass transition temperatures, improved thermal stability, and enhanced nanomechanical performance over pure PU. The NP-PUs demonstrated good selective inhibition of Candida albicans and Candida parapsilosis (30–55%) and no pronounced cytotoxicity to MRC5 human lung fibroblasts. Among the investigated AgFeO2@PEG/PUs, the best antifungal activity was shown by composites with 30 and 40 wt% soft segments. Consequently, the novel AgFeO2@PEG/polyurethane network nanocomposites could be further optimized to be used as biocompatible surfaces that also prevent formation of fungal biofilms.Graphical abstract

The effect of temperature and peroxides content on cross-linking and properties of EPDM-based rubber matrix

In this work, dicumyl peroxide (DCP), di-tert-butyl peroxide (DTBP), di(tert-butylperoxyisopropyl)benzene (DTBPIB), and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (DDTBPH) were used for cross-linking of rubber matrix based on Ethylene-propylene-diene monomer rubber (EPDM). The aim was to investigate the influence of curing temperature and the type and content of peroxide on curing process of rubber compounds, cross-link density, and physical-mechanical properties of vulcanizates. The results revealed that higher curing temperatures promote faster decomposition of organic peroxides, leading to the faster reactions of peroxide radicals with rubber chains. The increase in temperature resulted also in the increase of cross-linking degree. Although, side reactions as chain scission take over the main cross-linking reactions at very high temperatures resulting in the decrease of cross-link density. The increasing content of peroxides resulted in the acceleration of curing reactions and to increase of cross-link density. The fastest curing kinetics exhibited rubber compounds cured with DCP. However, vulcanizates cured with DCP were found to have the lowest cross-link density. In generally, the dependences of modulus, hardness, and elongation at break of vulcanizates were in line with the dependences of the cross-link densities, while higher tensile strength were found to have vulcanizates cured at higher temperatures and lower peroxides content.

Effect of polystyrene nanoplastics and their degraded forms on stem cell fate

Several studies have examined the effects of micro- and nanoplastics on microbes, cells, and the environment. However, only a few studies have examined their effects—especially, those of their reduced cohesiveness—on cell viability and physiology. We synthesized surfactant-free amine-functionalized polystyrene (PS) nanoparticles (NPs) and PS-NPs with decreased crosslinking density (DPS-NPs) without changing other factors, such as size, shape, and zeta potential and examined their effects on cell viability and physiology. PS- and DPS-NPs exhibited reactive oxygen species (ROS) scavenging activity by upregulating GPX3 expression and downregulating HSP70 (ROS-related gene) and XBP1 (endoplasmic reticulum stress-related gene) expression in human bone marrow-derived mesenchymal stem cells (hBM-MSCs). Additionally, they led to upregulation of MFN2 (mitochondrial fusion related gene) expression and downregulation of FIS1 (mitochondrial fission related gene) expression, indicating enhanced mitochondrial fusion in hBM-MSCs. Cell-cycle analysis revealed that PS- and DPS-NPs increased the proportion of cells in the S phase, indicating that they promoted cell proliferation and, specifically, the adipogenic differentiation of hBM-MSCs. However, the cytotoxicity of DPS-NPs against hBM-MSCs was higher than that of PS-NPs after long-term treatment under adipogenic conditions.

Colorimetric two-dimensional photonic crystal biosensors for label-free detection of hydrogen peroxide

Hydrogen peroxide (H2O2) detection is highly desirable for both environment and health concerns and a number of methods have been developed to monitor H2O2. However, most methods are limited due to the need of sophisticated instrument and high cost. Here we report a label-free two-dimensional (2-D) photonic crystal (PhC) horseradish peroxidase/bovine serum albumin (HRP/BSA) protein composite hydrogel sensor to monitor H2O2. Our 2-D PhC HRP/BSA protein composite hydrogel sensor is fabricated by mild protein cross-linking of BSA and HRP with glutaraldehyde, where BSA acts as a scaffold of HRP while HRP acts as the recognition molecule. The 2-D PhC HRP/BSA protein composite hydrogel sensor selectively detects H2O2 since HRP can specifically decompose H2O2 accompanying with heme inactivation. This protein hydrogel undergoes a volume phase transition as a result of peroxidase inactivation. The inactivation-induced conformational change of HRP gives rise to a decreased cross-linking density, which enlarges the particle spacing and decreases the Debye ring of the 2-D photonic crystals (PhCs). Our optimized 2-D PhC HRP/BSA-75 protein composite hydrogel sensors show a good linear range from 8.8 × 10-6 M to 60.6 × 10-6 M and an excellent sensitivity with a limit of detection of 8.8 × 10-6 M. This sensor fabrication method demonstrates the proof-of-concept for utilizing proteins with few lysine groups to develop smart PhC protein composite hydrogel sensors to determine H2O2 concentration in solution, which makes it possible for developing protein organogel sensors to detect gaseous H2O2 in the future.

Novel polyurethane network/organoclay nanocomposites: Microstructure and physicochemical properties

A series of novel polyurethane network/organoclay nanocomposites (PUN-NCs) with different soft segment contents (30–60 wt%) was prepared by in situ polymerization in solution and characterized. PU network (PUN) was made from poly(dimethylsiloxane)-based macrodiol as the soft segment and 4,4′-methylenediphenyldiisocyanate and hyperbranched polyester of the third pseudo generation as the hard segment. Nanocomposites were obtained by dispersion of organically modified montmorillonite (Cloisite 30B) nanofiller (0.5 wt%). The influence of the soft segment content on the functional properties of PUN-NCs was studied by Fourier transform infrared (FTIR), small-angle and near wide-angle X-ray scattering (SWAXS), thermogravimetric analysis (TGA), dynamic mechanical thermal analyses (DMTA), differential scanning calorimetry (DSC), nanoindentation, atomic force microscopy (AFM), scanning electron microscopy (SEM), and swelling behavior, water absorption and contact angle measurements. The biodegradation process was evaluated using mixed cultures of microorganisms that originated from soil. Mechanically strong PUN-NC materials in the form of films were obtained, pointing to good dispersion and the existence of exfoliated morphology of Cloisite 30B within the PUN matrix, and the nanocomposites with the abovementioned characteristics were obtained as a function of the soft segment content. The decrease of the soft segment content induced a higher degree of phase separated microstructure, increase of Young's modulus, hardness, plasticity, storage modulus, glass transition temperature, surface free energy and swelling ability in tetrahydrofuran, but at the same time, it is responsible for the decrease of crosslinking density and hydrophobicity of PUN-NCs. By choosing adequate soft segment content, the prepared materials can potentially be designed for coating applications, such as top coating materials in environmental conditions.

Investigating the Stress–Strain Behavior in Ring-Opening Metathesis Polymerization-Based Brush Elastomers

Brush networks are intriguing materials that are able to replicate the stress–strain behavior of soft tissue, but the effect of the backbone chemical composition on the network mechanics is largely unknown. Here, we show that brush elastomers made by ring-opening metathesis polymerization (ROMP) of norbornene-terminated poly(dimethylsiloxane) macromonomers are less extensible than brush elastomers with the methacrylate backbone yet not as extensible (λmax) as predicted by the strain-stiffening parameter (β) derived from fitting the experimental stress–strain curves. The softness (E0) and firmness (β) of the norbornene-based networks decrease with decreasing cross-link density as expected, but the λmax significantly drops when the grafting density becomes low enough, which has not been previously observed in this class of materials.